1. Field of the Invention
The present invention relates to a method and apparatus to record data on an optical recording medium, and more particularly, to a method and apparatus to record digital data by forming a mark on an optical disc.
2. Description of the Related Art
When recording data on an optical recording medium such as an optical disc, a mark is formed on a track formed in the optical disc. The mark is formed as a pit of a read only disc such as a CD-ROM, a DVD-ROM and the like. The mark is formed on a recordable disc such as a CD-R/RW, a DVD-R/RW/RAM and the like when a phase change occurs in a phase change layer, which is changed to be crystalline or amorphous depending on a temperature and coats of the recording layer.
Data recording methods include a mark edge recording method and a mark position recording method in view of a signal detection. In the mark position recording method, an amplitude of a detected radio frequency (RF) signal is changed from positive/negative to negative/positive in a position where the mark is recorded. In the mark edge recording method, the amplitude of the detected RF signal is changed from positive/negative to negative/positive at edges of the mark. Thus, it is important to accurately record the edges of the mark to improve a quality of a reproduced signal.
However, by observing a trailing edge of the mark recorded on the disc coated with the phase change layer according to a conventional recording method, it can be seen that a shape of the mark depends on a length of the mark or a distance between marks, i.e., a length of a space. In other words, the trailing edge is wider than a leading edge of the mark, which degrades recording/reproducing characteristics. A relatively long length of the mark further degrades recording/reproducing characteristics due to thermal accumulation.
FIG. 1A(a) shows a waveform of Non Return to Zero Inverted (NRZI) data, and FIGS. 1A(b) through 1A(d) show recording waveforms according to the conventional recording method. Referring to FIGS. 1A(b) through 1A(d), there are shown various recording waveforms to record the NRZI data shown in FIG. 1A(a). A first recording waveform of FIG. 1A(b) is for a DVD-RAM. Recording waveforms FIG. 1A(c) and FIG. 1A(d) are for a DVD-RW. T represents a cycle of a reference clock signal. According to the mark edge recording method, a high level of the NRZI data is recorded using marks and a low level of the NRZI data is recorded using spaces. A recording waveform used to record the mark is called “a recording pattern,” and the recording waveform used to form the space (erasing the mark) is called “an erase pattern.” Conventional recording waveforms FIG. 1A(b), FIG. 1A(c), and FIG. 1A(d) are each made of multiple pulses. A power level of each pulse is controlled to have one of four levels: Ppeak, Pb1, Pb2, and Pb3. As shown in section E, the power of the erase pattern is maintained to be a uniform predetermined DC level.
Because the erase pattern included in a conventional recording waveform is maintained at the uniform DC level for a predetermined time, heat of about 0-200° C. is continuously applied to a corresponding area. Thus, if the mark is recorded a plurality of times, the mark is degraded and the shape thereof is distorted. As a result, the recording/reproducing characteristics are remarkably degraded. In particular, the cycle T of the reference clock signal is reduced as a recording density and a linear velocity to record a large amount of data on a disc increases. As a result, the recording/reproducing characteristics are much more degraded when thermal interference between pulses constituting the recording waveform is increased.
FIGS. 1B and 1C show the shapes of marks formed on the optical recording medium. Referring to FIGS. 1B and 1C, a track of the optical recording medium includes a groove and a land. To record predetermined data on the optical recording medium, marks are formed on or erased from the groove and the land. However, a laser beam applies heat to the optical recording medium to form or erase the marks. The heat may cause a thermal crossing phenomenon in which adjacent tracks or adjacent marks are affected. FIG. 1B illustrates a method of recording the predetermined data by forming the marks on both the groove and the land where the thermal crossing phenomenon easily occurs. FIG. 1C illustrates a method of forming marks only on the groove, which is currently used for most optical recording media because the thermal crossing phenomenon hardly occurs. However, in the method shown in FIG. 1C, previously-formed marks may also be affected by applying too much heat when forming predetermined marks.
Different recording waveforms are used for different kinds of discs, i.e., DVD-RAM, DVD-RW, and the like because the characteristics of recording layers are different from each other. The use of different recording waveforms for different discs becomes a problem when manufacturing drives to record the data on different types of discs because drives that can read different types of discs should realize various recording waveforms, which increases costs.